1 FLT ATTENDANT AND 2 PAX WERE INJURED DUE TO SEVERE TURB DURING HIGH ALT CRUISE. THE FLT WAS APPROX 40 MI FROM ANY TSTM CELLS. FLC HAD GIVEN A PA ANNOUNCEMENT AND FASTEN SEAT BELT SIGN ON FOR EXPECTED TURB.

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1 FLT ATTENDANT AND 2 PAX WERE SLIGHTLY INJURED IN AN ENCOUNTER WITH SEVERE TURB; DEVIATING AROUND A LINE OF TSTMS AND WELL CLR OF THE WX WITH NO CELLS WITHIN 20 MI. IN ANTICIPATION OF POSSIBLE BUMPY RIDE A PA WAS MADE TO MAKE SURE PAX WERE IN SEATS AND SEAT BELT SIGN WAS ON. THE ENTIRE FLT FROM PIT-SAT HAD EXPERIENCED LIGHT TO OCCASIONAL MODERATE CHOP; SO WHEN THE FLT ATTENDANTS WERE BRIEFED ON POSSIBLE TURB I BELIEVE THEY THOUGHT IT WOULD BE MORE OF THE SAME RIDE CONDITIONS WE HAD ALREADY EXPERIENCED. THIS IS ALSO WHAT THE FLC ALSO BELIEVED SINCE WE WERE WELL CLR OF THE WX. THE SEVERE TURB ONLY LASTED FOR 3-5 SECONDS BUT WAS LONG ENOUGH TO THROW OUR 'B' FLT ATTENDANT IN THE AFT GALLEY TO THE FLOOR. 2 PAX ALSO COMPLAINED OF INJURIES. SINCE THE INJURIES WERE NOT SERIOUS WE CONTINUED ON TO OUR DEST WHERE THE FLT ATTENDANT AND PAX WERE TAKEN TO A LCL HOSPITAL; TREATED AND RELEASED. SUPPLEMENTAL INFO FROM ACN 367729: APCHED ANOTHER SMALLER LINE TO N AND WERE 40+ MI FROM CELLS ON EITHER SIDE WITH AN END TO THE NORTHERN LINE AHEAD AND A VERY OPEN AREA AHEAD INTO WHICH WE PLANNED TO TURN R (NW) AND MOVE OUT OF THE ENTIRE AREA OF CELLS. WE RECEIVED CONSTANT WX UPDATES FROM DISPATCH AND THEY RECOMMENDED AND AGREED WITH OUR PLANNED COURSE OF ACTION. WE REQUESTED RIDE RPTS FROM ATC (CTR) AND WERE TOLD ACFT AT FL330 AND FL370 HAD COME THROUGH EBOUND WITH PRETTY GOOD RIDES. WE ENTERED THE OPEN AREA; 40+ MI FROM THE NEAREST AND SMALLEST CELL. SUDDENLY HIT TURB APCHING SEVERE INTENSITY. MINIMAL GAIN/LOSS OF ALT +/-150 FT. PHYSICIAN PAX ATTENDED INJURED CREW. DISPATCH ARRANGED MEDICAL ASSISTANCE AT SAT. 2 PAX (1 NOT WEARING SEAT BELT) TREATED AND TAKEN TO HOSPITAL. FLT ATTENDANT TREATED AND WENT TO HOSPITAL ON OWN.